As our society ages, the number of patients confined to their beds is increasing. Such patients may require their upper body to be lifted to an upright position on his/her bed for a medical procedure or a meal, or for watching TV, reading a book, or a similar activity. There have accordingly been developed electrically operated beds, whose back bottom and knee bottom can be electrically raised or lowered. However, raising or lowering the back of the electrically operated bed result in the patient's body being subjected to a displacement or a force. A result is that a displacement occurs between muscles and skin, thin blood vessels connecting the muscles and skin are stretched so that the blood vessels become more susceptible to an obstruction or a circulatory disorder, and a skin disorder occurs. Also, when the body of a bedridden patient whose position has shifted due to back-raising and back-lowering needs to be returned to its original position by a carer, a large burden will be placed on the carer because the patient is unable to move on his/her own accord.
For other patients who are not bedridden, raising their upper body on a bed when they have to be moved from the bed to a wheelchair readily allows the patient to assume a seated position on the bed, which in turn allows them to move more readily to the wheelchair. It is again preferable for the patient's body not to be subject to any displacement or force when their upper body is being raised in such an instance.
Accordingly, there has been disclosed a method for controlling back-knee coordinated movement for an electrically operated bed with back-raising and knee-raising capabilities, in which the user-friendliness of the bed is improved by varying the timings of electrically driven back-raising and knee-raising motions, and ensuring that the angle between the back bottom and the knee bottom does not become smaller than necessary (Patent document 1).    Patent document 1: Japanese Laid-open Patent Publication No. 2001-37820    Patent document 2: Japanese Patent No. 3707555